A conventional wire cut electric discharge machine is operated such that a thin wire is used as an electrode and is kept taut, the wire and a workpiece are moved relative to each other, a voltage is applied between the wire electrode and the workpiece to generate an electric discharge, and the workpiece is melted by discharge energy, thereby performing electric spark forming. This operation is performed while a working fluid such as water is supplied to an electric spark forming region. The working fluid serves to insulate the wire electrode from the workpiece, eliminate powder from the melted workpiece, and prevent the wire from becoming disconnected due to heating of the wire by the electric discharge.
The working fluid is supplied by the mechanism shown in FIG. 1 to an electric spark forming region in a conventional wire cut electric discharge machine. Referring to FIG. 1, reference symbol W denotes a workpiece; and P, a wire electrode. Reference numeral 7 denotes an electric contact which is connected to a discharge current source E such as a capacitor charging circuit to supply the discharge current between the workpiece W and the wire electrode moving therethrough. Reference numeral 1 denotes a cylindrical nozzle for supplying the working fluid to the electric spark forming region between the workpiece W and the wire electrode P. The working fluid is supplied from a working fluid inlet port 4 to the electric spark forming region through a nozzle port 8. Reference numeral 2 denotes a cylindrical guide member for guiding the wire electrode P by a guide point 3. Reference numeral 5 denotes a cooling hole formed in the guide member 2 to receive the working fluid so as to cool the wire electrode P.
The nozzle 1, the guide member 2 and the like are vertically arranged such that the workpiece W is located thereabove, but below a second cylindrical nozzle 1'.
With the above arrangement, the working fluid is supplied from the working fluid supply port 4 to the nozzle 1 and sprayed from the nozzle port 8 to the electric spark forming region. The working fluid is also supplied from the wire electrode cooling hole 5 to the guide member 2 to cool the wire electrode P heated by discharge heat. The working fluid is then discharged from a hole 9 of a base 6.
According to the structure and operation described above, in order to increase the electric spark forming speed, the pressure of the working fluid is increased, and its flow speed is then increased, thereby easily eliminating powder deposited in a small gap between the wire electrode P and the workpiece W. However, in the conventional structure, even if the pressure of the working fluid is increased, the working fluid flows out from the holes 5 and 9. As a result, the pressure (i.e., the flow speed) of the working fluid in the electric spark forming region cannot easily be increased. When the size of the wire electrode cooling hole 5 is decreased to decrease leakage of the working fluid, thereby increasing the pressure and the flow speed of the working fluid to allow high speed electric spark forming, the amount of working fluid flowing into the guide member 2 through the wire electrode cooling hole 5 is decreased when the working fluid is supplied at a low pressure. As a result, the wire electrode P cannot be sufficiently cooled and may be disconnected, resulting in inconvenience.